The present invention relates to a method of signaling which data blocks can be combined together in a communication system consisting of a transmitter device and a receiver device. In particular, the present invention relates to such a method applied to combinable blocks transmitted in an incremental redundancy communication system.
The expression of combining as used in connection with the present application is intended to be understood as code combining. This means the combining of data (e.g. data bits) received via a channel during an original transmission together with the data (data bits) received via the channel during a retransmission of the data. After such a combining of data has been effected, channel decoding is performed based on the information from both transmissions and only then the received data block is checked for errors.
Furthermore, the expression incremental redundancy means a method of adapting a code rate, i.e. an amount of coding adopted in a communication system having a channel with varying transmission conditions.
Referring to a general example, a block of data is assumed to be coded with a code rate of xc2xd. Then, one half of this coded data is sent during an initial (original) transmission. At a receiver side, received data are perceived as having a code rate of {fraction (1/1)}. At a retransmission (if necessary upon failure in the original transmission), the other half of the coded data is transmitted, combined to the first half of the data block, and then a code rate of xc2xd is recognized at the receiver side. Such a combining then increases the amount of total coding in incremental redundancy systems.
FIG. 1 of the drawings illustrates a conventional transmission system denoted with numeral 1. Generally, a communication system 1 consists of a transmitter device 1A and a corresponding receiver device 1B. Transmission of data between these devices takes place via a transmission channel 1C established there between.
A communication method adopted by such a communication system is explained below with reference to FIG. 1, in which the respective steps are indicated by numbers (1) to (4). According to such a conventional communication method data are transmitted in units of blocks (also referred to as packetized data) via the channel with some channel coding. Namely, as indicated in step (1), a (first) data block #1 containing data X is sent from the transmitter device 1A to the receiver device 1B. If the receiver device 1B is not able to receive the transmitted block #1, a corresponding notification indicating this transmission error or failure, respectively, is returned to the transmitter device 1A. This notification is also called negative acknowledgment and represents a retransmission request upon a reception failure (step (2)). In response thereto, the transmitter device 1A in step (3) then transmits another block (data block #2) containing the same data X as contained in the (previous) data block #1. For this transmission, possibly an other coding can be used. The receiver device 1B in turn combines the data blocks received so far (step (4)), i.e. data block #1 is combined with data block #2, and tries to decode the retransmitted block again. This combining, as already mentioned above in connection with the general example, effectively increases the amount of total coding and thus decreases the probability of further errors.
However, since a subsequent data block containing the next data is only transmitted after a preceding block has been successfully transmitted or retransmitted, the whole communication procedure is somewhat delayed and the data rate that can be transmitted is reduced.
In order to reduce the delay and increase transmission rate, another prior art method and corresponding system has been proposed, according to which a plurality of blocks are transmitted in sequence without waiting for the respective acknowledgment. However, in such a situation, a retransmitted data block does not immediately follow the original one.
Consequently, the receiver device 1B of the communication system does not automatically know which data blocks can be combined with each other.
FIG. 2 schematically exemplifies a prior art method which has been developed to cope with this problem.
According to this known method, each data block B0, B1, . . . , Bn in the sequence of transmitted data blocks is assigned a sequence number or block number BN. In case there occurs an error in transmission or a reception failure in connection with an initial (first) or original transmission of a subject data block and a retransmission is requested, the retransmission is assigned the same number as the original transmission. The block numbers have to be coded more robustly, i.e. with higher redundancy, so that the probability that the receiver is unable to decode or recognize the block number is reduced to a minimum.
Thus, provided that the receiver device has received the block numbers, the blocks that have the same number can be combined with each other.
Specifically, with reference to the example of FIG. 2, a sequence of four data blocks containing data X, Y, and/or Z is transmitted at time instants 0, 1, 2, and 3. The first block B0 to which a block number BN of 546 has been assigned for the specific example, is assumed to have not been received correctly, so that its transmission has to be repeated.
The retransmission of said data block identified by BN=546 occurs at a time instant xe2x80x9c2xe2x80x9d. At this time, the block is retransmitted as indicated by the identical block number of BN=546 at time instant xe2x80x9c2xe2x80x9d and the data block contains the same data X as in the initial transmission at time instant xe2x80x9c0xe2x80x9d.
However, there is a disadvantage of this known method in that the amount of data that can be transmitted is reduced due to the additional overhead represented by the adopted block numbering which has to be transmitted in form of the block numbers BN together with each data block B0, . . . , Bn.
Moreover, even in case the transmission quality of the channel is as high that no errors occur, the block numbering still reduces the amount of user data that can be transmitted in the communication system.
Document EP-A-0 866 579 discloses the features of the preamble of claims 1 and 12, respectively. More precisely, also this document teaches that no serial or block numbers are transmitted to the receiver.
Furthermore, document U.S. Pat. No. 5,537,416 teaches to avoid to transmit location information or serial/block with each block.
Hence, it is an object of the present invention to provide a method of signaling which data blocks can be combined together in an incremental redundancy communication system consisting of a transmitter device and a receiver device, which is free from the above mentioned drawbacks and enables an increased data throughput. Moreover, it is an object of the present invention to provide a corresponding communication system.
According to the present invention, this object is achieved by a method of signaling which data blocks can be combined together in an incremental redundancy communication system consisting of a transmitter device and a receiver device, the method comprising the steps of transmitting said blocks from a transmitter device to a receiver device, with each transmitted data block including an information indicating whether a respective data block is transmitted for a first time or is a retransmitted block; checking, at said receiver device, whether the transmission of a respective data block has failed; requesting a retransmission of said data block from the transmitter device if said transmission of said respective block has failed, and in response to receiving said retransmission request at the transmitter device side, setting said information to a value indicating that said respective data block is a retransmitted block, and adding at least one header to said data block to be retransmitted, said header representing a reference to a physical location of an earlier transmission of said block in a sequence of transmitted blocks.
Also, this object is achieved by a communication system consisting of a transmitter device and a receiver device, each adapted to carry out the above method.
Favorable refinements of the present invention are as defined in the dependent claims.
Thus, according to the present invention it is advantageously possible to eliminate the need for each original block to contain block numbering information. Consequently, the previously present overhead due to block numbering can be significantly reduced, thereby increasing the user data throughput in the communication system. The only overhead needed in the original transmission of respective data blocks is a flag that can be represented by a single bit only. Thus, in case where a retransmission is not required, the overhead is reduced to a negligible and minimum overhead in the proposed incremental redundancy system.
The proposed method may further advantageously be applied to nearly any communication system in which data are transmitted in units of blocks or as so called packets.